chore(allsrv): inject id generation fn

Motivation for this change:

  1. we want determinism in tests, this allows for that
  2. we don't want the db owning the business logic of what an ID looks like
    a) if we switch out dbs, each db has to make sure its ID gen aligns... youch

Our tests are now fairly easy to follow. At this time, our `Server` is really
the owner of the id gen business logic. This is ok for now, but for more
complex scenarios, this can pose a serious problem.

allsrv/server.go

@@ -34,7 +34,7 @@ import (
 		a) there is nothing actionable, so how does the consumer know to handle the error?
 		b) if the APIs evolve, how does the consumer distinguish between old and new?
 	10) Observability....
-	11) hard coding UUID generation into db
+	✅11) hard coding UUID generation into db
 	12) possible race conditions in inmem store
 
 	Praises:
@@ -48,14 +48,31 @@ type Server struct {
 	db *InmemDB // 1)
 
 	user, pass string // 3)
+
+	idFn func() string // 11)
+}
+
+// WithIDFn sets the id generation fn for the server.
+func WithIDFn(fn func() string) func(*Server) {
+	return func(s *Server) {
+		s.idFn = fn
+	}
 }
 
-func NewServer(db *InmemDB, user, pass string) *Server {
+func NewServer(db *InmemDB, user, pass string, opts ...func(*Server)) *Server {
 	s := Server{
 		db:   db,
 		user: user,
 		pass: pass,
+		idFn: func() string {
+			// defaults to using a uuid
+			return uuid.Must(uuid.NewV4()).String()
+		},
 	}
+	for _, o := range opts {
+		o(&s)
+	}
+
 	s.routes()
 	return &s
 }
@@ -93,15 +110,10 @@ func (s *Server) createFoo(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	newFooID, err := s.db.createFoo(f)
-	if err != nil {
-		w.WriteHeader(http.StatusInternalServerError) // 9)
-		return
-	}
+	f.ID = s.idFn() // 11)
 
-	f, err = s.db.readFoo(newFooID)
-	if err != nil {
-		w.WriteHeader(http.StatusNotFound) // 9)
+	if err := s.db.createFoo(f); err != nil {
+		w.WriteHeader(http.StatusInternalServerError) // 9)
 		return
 	}
 
@@ -166,18 +178,16 @@ type InmemDB struct {
 	m []Foo // 12)
 }
 
-func (db *InmemDB) createFoo(f Foo) (string, error) {
-	f.ID = uuid.Must(uuid.NewV4()).String() // 11)
-
+func (db *InmemDB) createFoo(f Foo) error {
 	for _, existing := range db.m {
 		if f.Name == existing.Name {
-			return "", errors.New("foo " + f.Name + " exists") // 8)
+			return errors.New("foo " + f.Name + " exists") // 8)
 		}
 	}
 
 	db.m = append(db.m, f)
 
-	return f.ID, nil
+	return nil
 }
 
 func (db *InmemDB) readFoo(id string) (Foo, error) {

allsrv/server_test.go

@@ -18,7 +18,9 @@ func TestServer(t *testing.T) {
 	t.Run("foo create", func(t *testing.T) {
 		t.Run("when provided a valid foo should pass", func(t *testing.T) {
 			db := new(allsrv.InmemDB)
-			svr := allsrv.NewServer(db, "dodgers@stink.com", "PaSsWoRd")
+			svr := allsrv.NewServer(db, "dodgers@stink.com", "PaSsWoRd", allsrv.WithIDFn(func() string {
+				return "id1"
+			}))
 
 			req := httptest.NewRequest("POST", "/foo", newJSONBody(t, allsrv.Foo{
 				Name: "first-foo",
@@ -31,11 +33,8 @@ func TestServer(t *testing.T) {
 
 			assert.Equal(t, http.StatusCreated, rec.Code)
 			expectJSONBody(t, rec.Body, func(t *testing.T, got allsrv.Foo) {
-				assert.NotZero(t, got.ID)
-				got.ID = "" // this hurts :-(
-
 				want := allsrv.Foo{
-					ID:   "", // ruh ohhh
+					ID:   "id1",
 					Name: "first-foo",
 					Note: "some note",
 				}